<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        input:enabled{
            /* background: red; */
        }
        input:disabled{
            background: yellow;
        }
        input:focus{
            /*焦点*/
            background: blue;
        }
        input[type=checkbox]{
            /* 去掉默认样式 */
            appearance:none;
            width: 20px;
            height: 20px;
            border: 1px solid black;
        }
        input:checked{
            /*选项框选中的时候*/
            background: green; 
        }
        div::selection{
            /*选中后的样式*/
            background: yellow;
            color: red;
        }
    </style>
</head>
<body>
    <form action="">
        用户名<input type="text"><br>
        密码<input type="password"><br>
        记住用户名<input type="checkbox"><br>
        <input type="submit" disabled>
    </form>

    <div>Lorem ipsum dolor sit amet
         consectetur adipisicing elit.
          Voluptas, inventore.</div>
</body>
</html>